Method of sealing resistors



y 7 1 J. R. PIES 2,893,182

METHOD OF SEALING RESISTORS Filed Dec. 20, 1957 toinertgos -'5 l4 Esource l7 I6 2 Y INVENTOR JOHN R.P|ES

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ATTORNEY United States Patent METHOD OF SEALING RESISTORS John R. Pies,Dallas, Tex., assignor to Texas Instruments Incorporated, Dallas, Tex.,a corporation of Delaware Application December 20, 1957, Serial No.704,053

11 Claims. (CI. 53-22) This invention relates to a method for producinghermetically sealed resistors and in particular to a method of sealingresistors hermetically in an envelope containing an inert gas.

Heretofore the manner of sealing a resistor in an envelope filled withan inert gas has consisted of first forming and sealing an envelopearound the resistor, evacuating the envelope, adding an inert gas, andrescaling the envelope. The difilcult step in these operations is inevacuating the envelope so as to get all of the air out before insertingthe inert gas. Another diificulty with the aforementioned procedure isthatit is relatively expensive to mass produce resistors in thedescribed manner.

It has been discovered that by causing a heavy flow of the inert gasthrough a tube in which the resistor is placed prior to scaling that asuperior expulsion of the air is achieved. It has further beendiscovered that by maintaining a flow of the inert gas and by sealingthe tube at the end of the resistor remote from the source of inert gas,a quantity of this gas may be trapped within the tube to provide animproved packaged resistor upon sealing the nearer end.

Accordingly, it is an object of the present invention to provide asimplified method of insuring the complete removal of air from anenvelope which encloses a resistor.

Another object of the present invention is to provide a method ofproducing a resistor hermetically sealed in an inert atmosphere in amanner that lends itself to inexpensive mass production techniques.

A further object of the present invention is to provide a method ofproducing a resistor hermetically sealed in an inert atmosphere in whicha heavy flow of the inert gas is used to displace the air around theresistor before the sealing operation. 7

Other objects and advantages of the present invention will becomereadily apparent upon consideration of the following detaileddescription when taken in conjunction with the drawings in which:

Fig. 1 shows in a diagrammatic form a resistor placed in a glass tubeprior to the sealing operation;

Fig. 2 shows the same resistor with one end sealed;

Fig. 3 shows the same resistor sealed at both ends;

Fig. 4 shows in diagrammatic form an alternative embodiment of thepresent invention for holding a resistor and forming a seal; and

Fig. 5 shows a sectional view taken along 5-5 of Fig. 4.

Referring now to the drawings, Fig. 1 shows a tube holder which holdstubing 12. Extending through holder 10 is an inlet tube 11 for an inertgas such as helium, argon, or nitrogen. This tube extends through theholder 10 and within tubing 12. In the preferred form of the presentinvention this tubing 12 consists of a drawn tubular blank which has anecked down portion 13 preformed intermediate the two ends. A resistor14 provided with leads 16 and 18 is inserted into the tubular blank 12opposite open end 17 so that one end of the resistor14 abuts the neckeddown portion 13 and lead 16 ice of the resistor 14 is supported withinthe inert gas inlet tube 11on the other end as shown in Fig. 1. In thismanner resistor 14 is suitably held in place. Open end 17 provides anexhaust port for the inert gas.

A heavy How of the inert gas is introduced into tubing 12 through inlet11 effectively flushing out all of the air within the tube 12. Thisheavy flow of inert gas is caused by a pressure diiferential between thesource of the inert gas and the atmosphere within the tubing 12 in theorder of magnitude of from one-half to one p.s.i.

After flushing out the tubing 12 with the inert gas, the pressure isreduced to the level required to maintain a minimum forward flow of thegas. The reduced pressure required for this is in the order ofone-sixteenth to one-half psi. The reduced flow of the gas over resistor14 permits a seal shown at 21 in Fig. 2 to be made with relative ease.This sealing operation will be described presently.

The tubing 12 is heated by any suitable means such as by burner 20. Itis possible, for example, to obtain uniform heating of the periphery ofthe necked down portion 13 by rotating either the tubular blank 12 orthe burner 20. Alternatively, a ring flame may be employed which is ofsufiicient diameter to pass freely over the tubular blank 12.

After tubing 12 becomes pliable, portion 13 is further necked down byany suitable means. For example, the tubing may be grasped near open'end17 and pulled so as to stretch out and draw in the portion 13 and thenattached and sealed at 21 to lead 18 by continued heating by the heater20. Alternatively, a plurality of rollers may be used to contact thenecked down portion 13. The rollers are progressively moved inwardly andthey ultimately pinch ofli' the pliable material in the vicinity ofnecked down portion 13 to sever the tubular portion between necked downportion 13 and open end 17 from the remainder of the tubing 12. When theseal is made at 21, the flow of inert gas is stopped, but the reducedpressure is maintained. It can be seen that the preferred form oftubular blank 12 provides a shield for the lead 18 and the resistor 14from oxidation by virtue of the portion of the tube blank 12 betweennecked down portion 13 and the open end 17. Another advantage providedby the portion of the tube blank 12 between necked down portion 13 andopen end 17 is that it prevents stray gases from being introduced intothe vicinity of the seal 21 either by diffusion or by turbulence.

In Fig. 2 the next step of the complete sealing operation is shown asburner 20 begins to heat the tubing near the other end of the resistorwhich end is nearer the source of inert gas. Once again, when tubing 12has become pliable, it is necked down and sealed to a wire lead 16 asshown at 22 of Fig. 3. Similarly, during this operation a constantpressure of the inert gas is maintained against seal 21 so that whenseal 22 is made, an inert gas atmosphere is trapped around resistor 14.The encased resistor may now be removed to have its leads 16 and 18cleaned and dipped in solder or tin.

An alternative method in the formation of seal 22 is to introduce apartial vacuum into the closed portion of tubular blank 12. Fig. 4 showsschematically how this partial vacuum may be obtained. A pipe 17 isshown leading from the holder 10 to the source of inert gas. Suitablepumping means (not shown), which may be positioned either within holder10 or at the source of the inert gas, is used to withdraw by suctionsome of the inert gas from within the tubular blank 12a. It will beappreciated in this connection that suitable seals are provided bothbetween the inlet end of pipe 11 into holder 10 and between the holder10 and tubular blank 12a. Thus, the only inlet to the tubular blank 12ais through pipe 11, and the only exhaust from the tubular blank 12a isthrough the exhaust pipe 17. This reduced pressure may be maintained atthis stage of the operation because seal 21 has already been made andtherefore provides an enclosed working area. The use of a vacuum willtend to withdraw some of the inert gas that surrounds resistor 14.However, the vacuum used is not sufficiently high to withdraw all of theinert gas so that the end product obtained from this alternative methodwill contain a less dense inert atmosphere surrounding the resistor 14than those atmospheres produced by the previously described method. Anadvantage of using a partial vacuum in the sealing operation is that thereduced pressure facilitates the necking down in forming the seal 22. Inthis regard, it is to be noted that the ultimate desired pressure willbe a certain amount lower than the pressure at which the sealingoperation is performed because of gas expansion during the heat sealingand contraction thereafter upon cooling.

A still further modification is possible in the formation of the secondseal 22. In Fig. 4, a different shape for tubular blank designated 12ais shown. In this modification a necked down portion 13 is disclosed atthe end of the blank. By virtue of this, the blank itself may be shorterthan that previously described and consequently there will be lesswastage. However, there is a disadvantage in the use of a blank similarto that of 12a. Since there is a flow of gases under positive pressurethrough the tubing, there is a tendency for the inert gas to blow theflame from the burner 20 away. This disadvantage will not be present inthe preferred form of tubing 12 because the inert gases are preventedfrom blowing the flame away by the presence of the glass between neckeddown portion 13 and opening 17.

In Fig. 4, rollers 24 are shown which may be used to engage theperiphery of the glass tubing 12a and to mechanically roll the tubinginto a necked down position to assist in forming the second seal. Thismechanical rolling of the tubing is performed either simultaneously withthe heating of the tubing or immediately there after. This mechanicalworking of the tube 12a to provide a necked down portion may be used inconjunction with a partial vacuum within the tube as describedpreviously.

An additional modification shown in Fig. 4 is the disclosure of afriction holder 23 into which is inserted lead 16 of resistor 14.Friction holder 23 is supported within the outlet end of inert gas inlettube 11 in such a manner as to permit the inert gases to continue topass over the resistor 14 and to flush out the tubing 12a.

Fig. shows one embodiment in which a friction holder 23 may be supportedby legs 25 within the inert gas inlet pipe 11 so as to permit freeadmittance of the inert gas through passages 19. The lead 16 of theresistor is shown inserted within the central opening of friction holder23 which holder may be of rubber or 'other resilient material.

Kovar, Durnet or other wire leads that will fuse to glass is acceptablefor the resistor. In selecting the leads, however, it is desirable thatthe coefficient of thermal expansion of the wire be about equal to thatof the tubular blank. This is desired in order to reduce stress and toremove the possibility of cracking the tubular blank because of the widetemperature variation to which the' tubing is subjected.

In the preferred form of the present invention, the tubing blank isprepared from a typical glass of the type used for scaling to metalwhich includes heat resistant glass of the Pyrex type. However, othermaterials such as quartz glass or plastic materials may also be used.

Though the present invention has been shown and described in specificembodiments, various changes and modifications obvious to one skilled inthe art are within the scope, purpose and intent of this invention.

What is claimed is: Y

1. A method of sealing a resistor in an inert atmos- 4 r phere whichcomprises placing a resistor with a pair of leads attached theretowithin a tubular blank, expelling the air within said blank with aninert gas, heating said blank and sealing it to one of said leads on aside remote from the source of said inert gas while continuing the flowof said gas, heating said blank about the other of said leads adjacentsaid source of said inert gas and sealing said blank to said other leadthereby entrapping an inert gas atmosphere about said resistor.

2. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of leads attached thereto within atubular blank, expelling the air within said blank with a heavy flow ofan inert gas, heating said blank and sealing it to one of said leads ona side remote from the source of said inert gas while continuing adecreased flow of said gas, heating said blank about the other of saidleads adjacent said source of said inert gas and sealing said blank tosaid second lead thereby entrapping an inert gas atmosphere about saidresistor.

3. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of leads attached thereto within atubular blank that is provided with a necked down portion, supporting'said resistor by said necked down portion, expelling the air withinsaid blank with an inert gas, heating said blank and sealing it to oneof said leads on an end remote from the source of said inert gas whilecontinuing the flow of said gas, heating said blank about a second leadadjacent said source of said inert gas, and sealing said blank to saidsecond lead thereby trapping an inert atmosphere about said resistor.

4. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of:

leads attached thereto within a tubular blank that is provided with anecked down portion intermediate its ends, expelling the air within saidblank with an inert gas, heating said blank, shielding said resistorfrom a source of heat, sealing said blank to one of said leads on an endremote from the source of said inert gas while continuing the flow ofsaid gas, heating said blank about a second lead adjacent said source ofsaid inert gas, and sealing said blank to said second lead therebytrappingan inert gas atmosphere about said resistor.

5. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of leads attached thereto within atubular blank, expelling the air within said blank with an inert gas,heating said blank and sealing it to one of said leads on an end remotefrom the source of said inert gas while continuing the flow of said gas,heating said blank about a second lead adjacent said source of saidinert gas, drawing a partial vacuum within said blank to facilitatenecking down said blank about said second lead, and sealing said blankto said second lead thereby trapping an inert gas atmosphere about saidresistor.

6. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of leads attached thereto within atubular blank, expelling the air within said blank with an inert gas,heating said blank and sealing it to one of said leads on an end remotefrom the source of said inert gas While continuing the flow of said gas,heating said blank about a second lead adjacent said source of saidinert gas, mechanically working said blank to neck down said blank aboutsaid second lead, and sealing said blank to said second lead therebytrapping an inert gas atmosphere about said resistor.

7. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of leads attached thereto Within atubular blank that is provided with a necked down portion intermediateits ends, expelling the air within said blank with an inert gas, flameheating said blank and sealing it to one of said leads on an end remotefrom the source of said inert gas while continuing the flow of said gas,shielding the flow of inert gas from said flame to prevent said inertgas flow from blowing away said flame, heating said blank about a secondlead adjacent said source of said inert gas, and sealing said blank tosaid second lead thereby trapping an inert gas atmosphere about saidresistor.

8. A method of sealing a resistor in an inert atmosphere which comprisesplacing a resistor with a pair of leads attached thereto within atubular blank, supporting said resistor by a ,friction holder supportedwithin said blank, expelling the air Within said blank with an inertgas, heating said blank and sealing it to one of said leads on an endremote from the source of said inert gas while continuing the flow ofsaid gas, heating said blank about a second lead adjacent said source ofsaid inert gas and sealing said blank to said second lead therebytrapping an inert gas atmosphere about said resistor.

9. A method of sealing a resistor in an inert atmospherewhich comprisesplacing a resistor with a pair of leads attached thereto within atubular blank, expelling the air within said blank with an inert gas,and heating said blank and sealing it to each of said leads therebytrapping an inert gas atmosphere about said resistor.

10. A method of sealing a resistor in an inert atmosphere whichcomprises placing a resistor with a pair of leads attached theretowithin a tubular blank, expelling the air within said blank, introducingan inert atmosphere into said blank, and heating said blank and sealingit to each of said leads thereby trapping an inert gas atmosphere aboutsaid resistor.

11. A method of sealing a resistor in an inert atmosphere whichcomprises placing a resistor with a pair of electrical terminationsattached thereto within a tubular blank, expelling the air within saidblank, introducing an inert atmosphere into said blank, and heating saidblank and sealing it to each of said electrical terminations therebytrapping an inert gas atmosphere about said resistor.

No references cited.

